Printers have recently come to be used in a wider range of applications that is not limited to text and graphics, but also extends to photographic printing, and progressively higher levels of detail and clearly discernable printing are desired.
Enhanced printing precision is also desired in a light-emitting diode array used in the printer head of an LED printer, and techniques are being developed to meet the need for micro-fabrication and increased luminance of such light-emitting diode arrays.
However, the area of the light-emitting surface increases as a result of light leakage from the light-emitting portions of each of the plurality of light-emitting diodes that make up a light-emitting diode array when the light-emitting diode array is micro-fabricated and endowed with increased luminance. This light leakage significantly interferes with enhancing the degree of integration of the light-emitting diodes.
FIG. 9 is a schematic top view of a conventional mesa-isolated light-emitting diode array. This light-emitting diode array 101 is composed of a base 102 that includes a substrate, an N-electrode layer, a buffer layer, a distributed Bragg reflector layer, and an insulating film; a plurality of platform-shaped light-emitting units 103 that are isolated from each other by mesa etching and are provided to the upper surface portion; and P-electrode layers 104.
Each of light-emitting units 103 is square-shaped as viewed from above, and is configured so that a forward mesa surface and an inverted mesa surface are adjacent to each other at the corner portions on the four peripheral side surfaces of light-emitting units 103. The light-emitting units 103 are disposed at a prescribed interval in the transverse direction so that light emitting windows 111 in two positions thereof are adjacent to each other. P-electrode layers 104 are layers on the outside of the light-emitting units 103, are alternately drawn out in opposite directions at right angles to the positioning in the transverse direction of the light-emitting units 103 for each of the plurality of light-emitting diodes constituting the light-emitting diode array 101, and are connected to a bonding wide-area electrode.
FIG. 10 includes schematic views of the light-emitting diode, wherein FIG. 10A shows a top view of the light-emitting diode, and FIG. 10B is a perspective view of the same. In the light-emitting units 103, substantially square-shaped as viewed from above, mesa etching is performed so that the sides of the two light emitting windows 111 arranged in the transverse direction are inverted mesa surfaces, and the sides in the orthogonal direction are forward mesa surfaces.
The P-electrode layer 104 is I-beam-shaped as viewed from above, has the light emitting windows 111 in the open portions thereof, and extends from the center portion of the outside to form a bonding wide-area electrode. This P-electrode layer 104 also serves to block unnecessary light during light emission by the light-emitting unit 103 by covering the forward mesa surfaces on both sides and blocking light emitted from the forward mesa surfaces.
FIG. 11 is a top view showing the shape of the photomask 151 when the conventional light-emitting unit 103 is mesa-etched. The substantially square corners of the photomask 151 form right angles.
[Patent Reference 1]: Japanese Laid-open Patent Application No. 2001-177150